REPTILIA. 79 



ORDER I. CHELONIA.* 



Body oval, short, enclosed in a solid shell, covered by 

 skin, or with large scales; the upper part of the shell, com- 

 posed of dorsal vertebrae and ribs (as many as eight pair) 

 spread out and united together, is denominated the carapax; 

 the under part, formed generally of nine pieces, constitutes a 

 true sternum, and is called the plastron. A kind of frame 

 surrounds the carapax and joins it to the plastron at the sides ; 

 it is composed of a series of pieces, which appear to repre- 

 sent the sternal portion of the ribs. The scapula and bones 

 of the pelvis, instead of being attached to the ribs and dorsal 

 spine, are attached beneath, so that the Tortoise may be con- 

 sidered as an inverted animal. The vertebral extremity of 

 the scapula is articulated with the carapax ; the inferior ex- 

 tremity with two bones, of which one is analogous to the 

 coracoid apophysis of Birds and remains free, the other, rep- 

 resenting the clavicle, is united to the plastron ; so that the 

 two shoulders form a ring through which pass the oesopha- 

 gus and trachea ; jaws covered with horn as in Birds ; no 

 teeth ; heart composed of two auricles and of only one ven- 

 tricle, with two unequal communicating chambers. Four 

 remarkable genera. 



GENUS I. TBSTUDO, Brog. Land Tortoise. 



Feet adapted for walking ; legs as if truncated, with very 

 short toes closely joined as far as the nails, of which there are 

 five before and four behind. 



GENUS II. EMYS, Brog. Fresh-Water Tortoise. 



Toes more widely separated than in the preceding, and 

 more or less palmated ; carapax usually more flattened than 

 in the former. 



GENUS III. CHELONIA, Brog. Sea Tortoise. 



Feet elongated and flattened in the form of fins; toes 

 closely united in a single membrane ; shell too small to re- 

 ceive the head and feet. 



* Tortoises. 



